Dehydrochlorination of polychlorocyclohexanes



Patented Dec. 1 5, 1953 DEHYDROCHLORINATION F POLY- CHLOROCYCLOHEXANESDavid D. Humphreys, Baton Rouge, La., assignor to Ethyl Corporation, NewYork, N. Y., a corporation of Delaware No Drawing. Application NovemberSerial No. 259,281

5 Claims. (01. 260-648) This invention relates to thedehydrochlorination of organic chlorine compounds and more particularlyto a new and improved catalytic method for the dehydrochlorination ofbenzene hexachloride and similar compounds, characterized by an unusualand novel distribution of products.

The dehydrochlorination of benzene hexachloride has been traditionallycarried out by thermal treatment at temperatures in the vicinity of275-500" (3., usually in the presence of a catalyst, such as iron orferric chloride. This is a suitable method for the preparation oftrichlorobenzene, particularly when an outlet for the nongamma isomersof benzene hexachloride is thereby provided. However, this procedure isinefiicient in that large quantities of 1,2,3-trichlorobenzene, forwhich there exists no market outlet, are produced along with the desired1,2,4-isomer. The 1,3,5-isomer is produced only in negligible amounts.The dehydrochlorination product, therefore, must be either purified by adifficult and costly fractionation operation or the crude mixture mustbe sold at a reduced premium. Another disadvantage of this method isthat considerable carbonization of organic material takes place in thereaction zone. The carbonaceous material thereby formed is deleteriousto the process in that it tends to foul process equipment, it representsa loss of potential yield of dehydrohalogenation product, and itadversely affects the reaction rate and the efficiency of the catalystemployed. The above method of dehydrochlorination of benzenehexachloride is also deficient in that the reaction sequence cannot bestopped at any of the intermediate products, but always proceeds tocompletion, with the formation of trichlorobenzenes. Thus, valuablechemical intermediates and biocides present in the reaction mixture suchas 2,3,4,5,6-pentachlorocyclohexene-l are not recovered but areconverted to the completely aromatized end-products.

Another method used for the dehydrochlorination of benzene hexachlorideconsists of heating the benzene hexachloride with a solution of alkali,such as sodium hydroxide or potassium hydroxide. This procedure isextremely inefiicient in that the valuable hydrogen chloride produced inthe dehydrochlorination is converted by the action of the alkali intorelatively valueless sodium chloride or potassium hydroxide,respectively.

In the formation of benzene hexachloride by additive chlorination ofbenzene, varying amounts of monochlorobenzene hexachloride and dichlo- 2robenzene hexachloride are Thelddehydrochlorination normally formed. wouead to the formation of valuable ucts, such as tetra h prodmbenzeneclorobenzenes and pentach1o-- A principal object of my invention is toprovide a new and improved meth g f o r tii e dehydrochlorination ofpolychlorocyclohexanes Another ob ect is to provide a catalytic processfor produc1ng a mixture, of trichlorobenzene in l,2,4-tr1chlorobenzenepredominates over agfiieviighlorobenzene to a degree not heretoforeAnother object is to provide a metho drochlorinating benzenehexachloride v v e ar y a preponderant amount of 1,2,4-trichlorobenzenetogether with 2,3,4,5,6-pentach10r0cyc10hexene-1 is formed. Anotherobject is to provide a prac ticable means of producing2,3,4,5,6-pentach1orocyclohexene-l by the dehydrochlorination of benzenehexachloride. Still another object is to provide a method for increasingthe rate of dehydrochlorination of benzene hexachloride. A further obect is to provide a method for the dehydrochlorlnation of benzenehexachloride in which hydrogen chloride in high purity is produced asone of the products. Still another obiggrioscfi provide a practicablemeans for the deorma ion of anIdIpctachlorocyclohexari f ave discoveredthat polychloroc clohex such as benzene hexachloride, can be readily a iiil ei iiciently catalytically dehydrochlorinated at a high reactionvelocity to yield mixtures of isomeric polychlorobenzenes by contactingthe polychlorocyclohexane;with a selective, highly specific catalyst, asdescribed hereafter. In the case of benzene hexachloride, the proportionof" l, 2,4-trichlorobenzene in the product is markedly higher than hasbeen obtained heretofore. Moreover, my invention can be carried out so,that under certain conditions substantial quanti ties ofpolychlorocyclohexenes are obtained. The

production of cyclic olefins under conditions;

which permit them to be isolated before beingfurther dehydrochlorinatedis an important feature of my invention.

By benzene hexachloride I mean either a total. stereoisomeric mixture of1,2,3,4,5,6-hexachloro-- cyclohexanes, such as is produced in theadditive" chlorination of benzene (hereafter designed as:

.crude benzene hexachloride), or any of the in-- dividual1,2,3,4,5,6-hexachlorocyclohexane stereo-- isomers or any mixture of twoor more of the-- stereoisomeric l,2,3,4,5,6 hexachlorocyclohexanes,including'amixture such as that arising:

of these compounds" amples herein.

3 when the gamma isomer has been removed from a total stereoisomericmixture.

The catalysts which are suitable for use in my process comprise organicsulfonic acids.

When I contact benzene hexachloride as herein defined at a temperatureof at least 180 C. with catalytic quantities of one of the specific andselective catalysts described above, I smoothly produce mixtures of1,2,4-trichlorobenzene and 1,2,3-trichlorobenzene inwhich-tharatio ofthe commercially important lfzflieisomer ,to 1,2,3-isomer is as high as175 per cent of the ratio obtained when old methodsare used. Whenbenzenehexachloride is dehydrochlorinated=bynther mal treatment in the absenceof a. catalyst the dehydrochlorination rates are greatly .depressedbelowthose in my process. I obtain equally advantageous results with otherpolychlorocyclohexanes, as enumerated herein.

Example 1 illustrates one manner in which my inventi n inla practicedandalso points out the advantages .andbenefits .oimc'xinvention. .Allpart and p r en a es :are 'by weight i all ex- Example I :.'Ioarreaction wessel equipped with a mechanical agitator, a temperaturemeasuring device and a packed distillation column was charged 100 .parts:by weight: of crude bcnzene hexachloride and one part1by weight o'i=p-toluenesulfonic acid. :To the :top .of the=packed idistlllingcolumnwas connected a condenser, a variable take-ofi'distilling headcontaining 'a-.temperature measuring device, a distillate -co'oler,and=a rtared hydrogen 5 chloride absorber containing sodium hydroxidesolution.

The reaction wessel was heated by controlled external means, and theagitator: was started as -soon-as the charge was *fluidenough'tobe-stirred. The reaotion-wasmonsideredto havestarted when"hydrogen chloride fumes were observed. -A-fter a substantial reflux in-the distillation column wasestablishedjdistillate was taken off at arate =suffioient to maintain the reactor temperatureat 300-350 during'the --maj or part of =the run.

"The rateof dehydroohlorination was=determined by periodio-wei ghing oftheamount of hydrogen chloride absorbed hy the sodium hydroxide in thehydrogen chloride absorber. reaction tima thatiis, .the time -requiredfor evolution of per cent of the theoretical amount of hydrogen chlorideor complete conversion of 'the benzenehexachloride -to*trichlorobenzene,

was used as-the criterion for velocityof the -de- 4 The 50=per cent 4lenesulfonic acid, 2-naphthalenesulfonic acid, 1,4-naphthalenedisulfonicacid, toluene-w-sulfonic acid, taurine, 3-aminopropane-1-sulfonic acid,decanesulfonic acid, isethionic acid and others thereof, sulfoaceticacid, ethane-1,2-disulfonic acid, anthraquinone-l-sulfonic acid,mbenzenedisulfonic acid, .ethylbenzene-p-sulfonic acid,2-chlorotoluene-5-sulfonic acid, mahogany ,acids and the like are usedin place of p-toluenesulfonic acid equally beneficial results areobtained. Many of these compounds are not easily obtainable as the freeacid, but are obtained in the formof metal or amine salts. The salts areof equal applicability in my invention, since under my reactionconditions they are converted to {the free acids. Among the catalystsherein described, I prefer to use lower arylsulfonic acids such asbenzenesulfonic acid and p-toluenesulfonic'aoid since these catalystsare the most economical.

In :order that the contrast between my inventionand prior means may berealized the ,fol- :lowing examplepresents results obtainedwhen powdered:iron is used ,as the catalyst.

Example .II

Using the same procedure as in Example I, a mixture-of parts of crudebenzene .hexachloride and 3 partsof powdered ironwas heated-:to a

reactor temperaturecf 285-300 C. The '50 per lystthe 50 per centreactiontime is-sloweddown to 63 minutes.

My invention maybe carried out aseithera batch-process or-a continuousprocess. .Onevaria- -tion ofbatch operation'has beendescribed inExampleI, above.

In the continuous embodiment, which is the preferred embodimentof myinvention, molten or solid polychlorocyclohexane is continuously chargedto a-pot-type vessel or tube-type vessel containing a-chargeof catalystor, alternatively, polychlorocyclohexane and catalyst can be charged totllBW'QSSGl concurrently. Heat is applied to the vessel, and reactionproducts are continuously removed and recovered :from the reactionmixture by distillation and-subsequent condensation. Hydrogen chlorideis continuously removed and collected in a hydrogen chloride scrubber.The mixture of products whichcomprisesthe distillateis resolved byfractional distillation or other means.

My-invention is operable over a'wide range or temperatures. Temperaturesof at-least about 180 C. are preferably-employed. Generally, in order toavoid excessive losses o1 polychlorocyclo- 'hexane'by boiling, thetemperature should be not higher'thanabout 350 C. 'In the preferredprocess applications of my invention, I remcvethe liquid productsproducedby continuous distillation from the reaction mixture. 'Since theboilmg point of 1,2,4-trichlorobenzene at normal pressure is about-213'C. and that of 1,2,3-trichlorobenzeneis about 219 C,, Ipref er tooperate at atemperature of at least about 220 0.

My preferred range of temperature,therefore lies between about 220 C.and 350 C. h

The amount of catalyst employed can'be varied between a verylowpercentage, such as aboutllOl per cent of the weight'of benzene hexachloride to about lilper cent of the weight of benzene hexachloride.However, percentages greater than about 2 per cent of the weight ofbenzene hexachloride provide only minor additional benefits, so I preferto use proportions of catalyst not greater than about 2 per cent of theweight of benzene hexachloride being reacted.

I claim: 1. A process. for the dehydrochlorination of apoiychlorocyclohexane comprising contacting said polychlorocyclohexaneat an elevated ternperature with a catalytic amount of a sulfonic acid.

2. The process of claim 1 further defined in that thepolychlorocyclohexane is benzene hexachloride.

3. A process for the dehydrochlorination of a polychlorocyclohexanecomprising contacting said polychlorocyclohexane at a temperature of atleast 180 C. with a minor quantity of sulfonic acid.

4.A process for the dehydrochlorination of a polychlorocyclohexanecomprising contacting said polychlorocyclohexane at an elevatedtemperature with a sulfonic acid, the ratio of saidpolychlorocyclohexane to said sulfonic acid initiaily present being atleast 9 to 1.

5, A process for the dehydrochlorination of a polychlorocyclohexanecomprising contacting said polychlorocyclohexane at a temperature of220-350 C. with an arylsulfonic acid.

DAVID D. HUMPHREYS.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 1,872,700 Dreyfus M Aug. 23, 1932 2,042,223 Groll et a]. May26, 1936 2,569,441 Alquist et a1 Oct. 2, 1951

1. A PROCESS FOR THE DEHYDROCHLORINATION OF A POLYCHLOROCYCLOHEXANECOMPRISING CONTACTING SAID POLYCHLOROCYCLOHEXANE AT AN ELEVATEDTEMPERATURE WITH A CATALYTIC AMOUNT OF A SULFONIC ACID.